The invention relates generally to a fluid control system and, more particularly, to a swing control algorithm for a hydraulic circuit.
Conventional hydraulic systems, for example, those implemented in large excavators, typically include an open center system to control swinging movement of an arm attached to a cab, for example. Such a system is commonly referred to as a swing circuit. In contrast, a closed center system is typically used to control implements. In such hydraulic systems, the open center system and the closed center system each include a dedicated pump; a fixed displacement pump for the open center system and a variable displacement pump for the closed center system. The open center system provides the operator with a feel for how much of a load is on the swing circuit motor, whereas the closed center system does not. However, the open center system is generally less efficient than a closed center system because some fluid flow in the open center system usually gets to tank without performing any work.
One typical hydraulic swing circuit, as shown in U.S. Pat. No. 5,575,149, includes an open center system with a fixed displacement pump. This swing circuit employs a control valve, a pair of pilot operated, dual level pressure relief valves, and a pair of pilot operated counter balance valves. The circuit does not provide a mechanism for assisting with determination of when the arm controlled by the swing circuit runs up against a wall. In addition, such a complex system that lacks the efficiency of a closed center system may not be desirable.
A fluid control system and swing control algorithm for effectively and efficiently providing an open center feel to a closed center hydraulic system is desired. The present invention is directed to solving one or more of the problems set forth above.
According to one aspect of the invention, a fluid control system operative to control rotational movement of a swing structure and movement of at least one implement may comprise a pump, a tank, and an actuator including a working chamber. A valve assembly may be configured to control fluid communication between the working chamber and the tank and to control fluid communication between the working chamber and the pump. An input device may be operative to selectively control movement of the swing structure. The system may include a controller in communication with the valve assembly and the input device. The controller may be configured to control a flow condition of the working chamber through a sensed pressure condition of the working chamber and a command from the input device.
According to another aspect of the invention, a method is provided for controlling a hydraulic system. The method may include receiving an input command from an input device, generating a desired pressure value based on the input command, generating a flow limit based on the input command, and causing incremental movement of an actuator. A magnitude of the movement over a predetermined time interval may be based on the desired pressure value and the flow limit.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.